[ReactNative] Remove unused executor context id

Summary:
Remove `RCTGetExecutorID` and `RCTSetExecutorID`, it wasn't used anymore since
the bridge was refactored into `RCTBridge` and `RCTBatchedBridge`.

Examples/UIExplorer/UIExplorerUnitTests/RCTBridgeTests.m

@@ -24,7 +24,7 @@
 
 @property (nonatomic, strong, readonly) RCTBridge *batchedBridge;
 
-- (void)_handleBuffer:(id)buffer context:(NSNumber *)context;
+- (void)_handleBuffer:(id)buffer;
 - (void)setUp;
 
 @end
@@ -57,7 +57,6 @@ RCT_EXPORT_MODULE()
 - (void)executeJSCall:(__unused NSString *)name
                method:(__unused NSString *)method
             arguments:(__unused NSArray *)arguments
-              context:(__unused NSNumber *)executorID
              callback:(RCTJavaScriptCallback)onComplete
 {
   onComplete(nil, nil);
@@ -155,7 +154,7 @@ RCT_EXPORT_MODULE(TestModule)
   NSArray *args = @[@1234, @5678, @"stringy", @{@"a": @1}, @42];
   NSArray *buffer = @[@[testModuleID], @[testMethodID], @[args], @[], @1234567];
 
-  [_bridge.batchedBridge _handleBuffer:buffer context:RCTGetExecutorID(executor)];
+  [_bridge.batchedBridge _handleBuffer:buffer];
 
   dispatch_sync(_methodQueue, ^{
     // clear the queue

Examples/UIExplorer/UIExplorerUnitTests/RCTContextExecutorTests.m

@@ -33,7 +33,6 @@
 {
   [super setUp];
   _executor = [[RCTContextExecutor alloc] init];
-  RCTSetExecutorID(_executor);
   [_executor setUp];
 }
 
@@ -139,7 +138,6 @@ static uint64_t _get_time_nanoseconds(void)
           [_executor executeJSCall:@"module"
                            method:@"method"
                         arguments:params
-                          context:RCTGetExecutorID(_executor)
                          callback:^(id json, __unused NSError *unused) {
                            XCTAssert([json isEqual:@YES], @"Invalid return");
                          }];